As is well known, liquid or water of an aquarium must be maintained substantially free of organic-based materials, such as excess fish food, excrements and other contaminants which may be damaging to aquatic life. Several different types of filters and aerators have been developed which have met with varying degrees of success in maintaining the desired water conditions. However, these in general have not proven to be entirely satisfactory, either because they do not have sufficient water circulation capacity, require regular replacement of all of the water in the tank, or are too expensive to manufacture, too costly to operate or too difficult to clean.
One type of system that has been used for filtering and aerating an aquarium, particularly the small-capacity type as found in homes, is an air circulation system. An example of an air circulation system is disclosed in U.S. Pat. No. 3,294,239, wherein a pressurized supply of air is delivered to a lower chamber where air is introduced into the liquid by surface contact. An air pump then draws the air from the lower chamber and water from the tank into a tube for mixture, which is then delivered through a filter into the tank. This type of system relies to a large degree upon the absorption of the air into the water by increasing the air/water surface contact area within the tank. Thus, the primary oxygen supply into the liquid is by absorption.
Another air-type filtering system is disclosed in U.S. Pat. No. 3,490,416, wherein an elongated apertured tube is located in a confined area adjacent the bottom of an aquarium to introduce air bubbles into the liquid to aerate the water and provide a high percentage of oxygen saturation. As a result of the flow of the air bubbles, the water is circulated through a filtering system to provide filtration and purification of the water.
In such a system, it is easy to supply an adequate amount of oxygen to support aquatic life. However, in such systems, it is difficult to maintain a proper environment to remove the excess food, waste materials and excrements from the water. While such materials may be collected in a filter, which is normally part of such a system, the filter requires frequent replacement, which not only is costly but also is time consuming for the owner.
In most filtering systems, aerobic bacteria is developed on the filter bed or filter element which is designed to destroy waste and purify the water. However, with the very limited circulation of the water in the system, such as disclosed in U.S. Pat. No. 3,294,239, it is very difficult to produce an effective and efficient bacterial action which will dispose of the wastes in the water. Thus, in many instances, the filter must be frequently replaced and, in addition, the water in the aquarium tank will have to be replaced with fresh water.
Another type of system is what may be referred to as a "water pump-induced circulation system", is considered to be much more efficient than an air-induced circulation system. In the water pump system, the pump has an impeller element which exerts force directly on the incompressible fluid and thus forces the entire body of water in the tank through the filter, thereby eliminating the need for reliance upon gravitational forces, expansion of air bubbles and other hard to control factors. An example of such type of system is disclosed in U.S. Pat. No. 3,722,685 wherein a lower chamber is defined in the bottom of the aquarium tank and has a centrifugal water pump located therein which draws water from the chamber and circulates the water through a filter that is located above the water level for easy access for replacement. The cleansed water, after passing through the filter, is returned to the bottom chamber within the tank. This system is designed for a large capacity pump to draw from the bottom of the tank through the upper exposed filter. Again, with such a system, it is extremely difficult to provide proper oxygen supply into the liquid in the tank to support aquatic life because the oxygen is supplied to the water by absorption at the surface.
Other more elaborate types of aeration and filtering systems have been developed, such as for example shown in U.S. Pat. Nos. 3,418,973; 3,971,338 and 4,098,230. However, most of the prior art known systems are either too costly to manufacture and/or too costly to maintain.